Posted
by
timothy
on Thursday December 17, 2009 @09:48PM
from the next-time-send-chocolate dept.

The Bad Astronomer writes "NASA's Cassini spacecraft took an image of Saturn's giant moon Titan earlier this year that serendipitously provides proof of liquid(probably methane) on its surface. The picture shows a glint of reflected sunlight off of a monster lake called Kraken Mare (larger than the Caspian Sea!). Scientists have been getting better and better evidence of liquid methane on Titan, but this is the first direct proof."

Prior to this, the main evidence that Titan might have liquid methane was based on the reflection of radio waves detected by the Cassini probe. In particular, there were discrepancies between what one would expect and what was observed in the percentage of reflection in the ELF range (about 2 to 30 Hz). This discrepancy suggests some form of boundary layer, such as a boundary between liquid and solid methane or between liquid methane and some other solid substance. There's also a lot of evidence for a large internal methane sea under the solid surface. We still know very little about Titan. We've only sent a single probe (Huygens) actually dedicated to investigating it. However, even Huygens wasn't much and was just a part of the larger Cassini mission. The next scheduled mission is the TSSM (Titan Saturn System Mission) (http://en.wikipedia.org/wiki/Titan_Saturn_System_Mission [wikipedia.org] http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=44033 [esa.int]) which will focus a lot more on Titan. Hopefully a lot of the mysteries about the moon will then be answered.

Titan is routinely used as an example of a moon that might have life. Unfortunately, if there is any life, it is almost certainly microbial. So no one is appreciating the view from the planet.

We know that Titan has a lot of methane. The main reason is that the radiation it gives off is consistent with methane. In particular, we can use spectroscopy to confirm that the light given off is highly consistent with methane reflecting light from the sun. See http://en.wikipedia.org/wiki/Spectroscopy [wikipedia.org]. We have evidence for the methane nature both in the visible range, infrared range and certain other ranges that is consistent with methane and not much else. Moreover, methane is very stable and fairly common (as chemicals go) so even if we didn't have very good spectroscopic data, it would be the most likely guess.

This image was taken by Cassini, the US probe currently orbiting Saturn. http://www.nasa.gov/mission_pages/cassini/multimedia/cassini20091217.html [nasa.gov] Issues in our own atmosphere thus could not impact this. And if you meant that Titan might have strange atmospheric behavior causing this, that's almost as unlikely. The size of this event is much larger than almost any weird atmospheric event (which are normally at most a few hundred meters large at the very largest, rather than many kilometers across. Moreover, this picture isn't the only data point. The data was consistent with specular reflection over all observed wavelengths (both visual and near infrared). So you would need to posit an extremely large event that happened to precisely duplicate what we'd expect to see in reflection. That's remotely possible, but not at all likely. There's never "proof" in science. Proof is for mathematics and alcohol. But this is very strong evidence for the presence of a large body of liquid methane on the surface of Titan.

The Huygens probe was actually designed to float in liquid in case it encountered a pond, lake, or ocean. It would have been interesting if it did, but alas it landed on just dry land (or at least frozen-solid land). However, the rocks (possibly water-ice) it imaged at the surface were rounded off, suggesting that they used to be embedded in liquid.

Methane is the precursor to organic molecules, in a more general sense, not the result of biological processes. When you're the simplest combination of carbon (what, the fourth most abundant element in the universe?) and hydrogen (the most abundant element), it's hard to argue that your existence requires biological processes. (Particularly as methane is found everywhere volatiles can be found in our solar system and outside of it.)

Perhaps you're confused by the fact that methane on Earth is usually the result of biological activity? That's because in our peculiar atmosphere, methane can't survive long before oxidation.

Even if Diopter was a proper measure of length (and it isn't), it would actually be 1/(10^-12 Diopter) as Diopter is the reciprocal of a focal length to measure optical power. Still, it's an interesting way of putting it.

I'm afraid you are being pedantic. Both are acceptable. The "-re" suffix is an influence from French. If you look at French words for measuring devices as well as units of measure, you will understand this.

Lets try to find life that has nothing to do with the life we know and endure on this planet and would die if it tried to live amongst us.

No. What you are saying is basically, "We should be looking for something we can't imagine." I'd like to point out that this is basically the same as saying "Let's find some shit," and doesn't help whatsoever in directing us WHERE we ought to be looking for life. If you want to find life, you need some kind of strategy to narrow down the billions of possible places to look to something that's likely to turn up some results. Looking for something that, by definition, you have no idea how to look for, is not a fruitful use of resources.

Water, carbon, nitrogen, these are not rare materials in the universe. Chances are pretty good that if life could form from these materials here, it could form elsewhere. And we know WHAT to look for to recognize the signs of life as we know it. Only if we look long and hard, and find no signs of life as we know it anywhere in the measurable universe, should we turn to such vague propositions as "Let's look for something we can't imagine."

I happen to have been tech resp. of the european Huygens probe that Cassini brought to Titan, and what I remember the most from the time of Huygens descent and landing years ago, is this feeling that all the active descent has *already* happened, while here on Earth we didn't yet have received the first bits of info, radiowave that were still into the travel.

Indeed that was a very real way of measuring distance. Saturn definitely is not close...

indeed on Titan the ground rocks are constituted of almost pure water ice, and over there ice just will be rock-hard forever.The pebble on these Cassini-Huygens lander photos are ice: http://www.esa.int/SPECIALS/Cassini-Huygens/SEMEMY71Y3E_0.html [esa.int] (visible on the orange vertical image that is the "last photo" Huygens took once on ground)Hervé

There's plenty of oxygen on Titan. The whole crust is made out of water ice. True there is no free molecular oxygen, but neither was there on Earth before about a billion years ago.

As for life on Titan, the suggestion is that there might be an opportunity when the liquid water beneath Titan's 50-km-thick ice crust bubbles to the surface (a "cryovolcano"), or when a meteor impact leaves a patch of melted local bedrock (which is water ice, so the patch would be a lake). When liquid water from one of these sources combines with the organics in the atmosphere, who knows what happens. But it better happen fast -- the whole thing freezes over in 10^4 years!